Problem: Khan.scratchpad.disable(); To move up to the maestro level in his piano school, Luis needs to master at least $87$ songs. Luis has already mastered $18$ songs. If Luis can master $4$ songs per month, what is the minimum number of months it will take him to move to the maestro level?
Explanation: To solve this, let's set up an expression to show how many songs Luis will have mastered after each month. Number of songs mastered $=$ $ $ Months at school $\times$ Songs mastered per month $+$ Songs already mastered Since Luis Needs to have at least $87$ songs mastered to move to maestro level, we can set up an inequality to find the number of months needed. Number of songs mastered $\geq 87$ Months at school $\times$ Songs mastered per month $ +$ Songs already mastered $\geq 87$ We are solving for the months spent at school, so let the number of months be represented by the variable $x$ We can now plug in: $x \cdot 4 + 18 \geq 87$ $ x \cdot 4 \geq 87 - 18 $ $ x \cdot 4 \geq 69 $ $x \geq \dfrac{69}{4} \approx 17.25$ Since we only care about whole months that Luis has spent working, we round $17.25$ up to $18$ Luis must work for at least 18 months.